Gawne Timothy J, Ward Alexander H, Norton Thomas T
Department of Optometry and Vision Science, University of Alabama at Birmingham, Birmingham, Alabama *
Optom Vis Sci. 2018 Oct;95(10):911-920. doi: 10.1097/OPX.0000000000001283.
In spectrally broad-band light, an emmetropization mechanism in post-natal eyes uses visual cues to modulate the growth of the eye to achieve and maintain near emmetropia. When we restricted available wavelengths to narrow-band blue light, juvenile tree shrews (diurnal dichromatic mammals closely related to primates) developed substantial refractive errors, suggesting that feedback from defocus-related changes in the relative activation of long- and short-wavelength-sensitive cones is essential to maintain emmetropia.
The purpose of this study was to examine the effects of narrow-band ambient blue light on refractive state in juvenile tree shrews that had completed initial emmetropization (decrease from hyperopia toward emmetropia).
Animals were raised in fluorescent colony lighting until they began blue-light treatment at 24 days of visual experience, at which age they had achieved age-normal low hyperopia (mean ± SEM refractive error, 1.2 ± 0.5 diopters). Arrays of light-emitting diodes placed atop the cage produced wavelengths of 457 (five animals) or 464 nm (five animals), flickered in a pseudo-random pattern (temporally broad band). A third group of five animals was exposed to steady 464-nm blue light. Illuminance on the floor of the cage was 300 to 500 human lux. Noncycloplegic autorefractor measures were made daily for a minimum of 11 days and up to 32 days. Seven age-matched animals were raised in colony light.
The refractive state of all blue-treated animals moved outside the 95% confidence limits of the colony-light animals' refractions. Most refractions first moved toward hyperopia. Then the refractive state decreased monotonically and, in some animals, passed through emmetropia, becoming myopic.
From the tree shrew cone absorbance spectra, the narrow-band blue light stimulated both long-wavelength-sensitive and short-wavelength-sensitive cones, but the relative activation would not change with the refractive state. This removed feedback from longitudinal chromatic aberration that may be essential to maintain emmetropia.
在光谱宽带光下，出生后眼睛的正视化机制利用视觉线索来调节眼睛的生长，以实现并维持近似正视状态。当我们将可用波长限制为窄带蓝光时，幼年树鼩（与灵长类密切相关的昼行性双色哺乳动物）出现了明显的屈光不正，这表明长波长和短波长敏感视锥细胞相对激活中与离焦相关变化的反馈对于维持正视状态至关重要。
本研究的目的是检查窄带环境蓝光对已完成初始正视化（从远视向正视降低）的幼年树鼩屈光状态的影响。
动物在荧光群体照明下饲养，直到它们在视觉经验24天时开始蓝光治疗，此时它们已达到年龄正常的低远视（平均±标准误屈光不正，1.2±0.5屈光度）。放置在笼子顶部的发光二极管阵列产生457（五只动物）或464nm（五只动物）的波长，以伪随机模式闪烁（时间上宽带）。第三组五只动物暴露于稳定的464nm蓝光下。笼子底部的照度为300至500勒克斯。每天进行至少11天至最多32天的非散瞳自动验光测量。七只年龄匹配的动物在群体照明下饲养。
所有接受蓝光治疗的动物的屈光状态都超出了群体照明动物屈光的95%置信限。大多数屈光首先向远视移动。然后屈光状态单调下降，在一些动物中，经过正视状态，变为近视。
从树鼩视锥细胞吸收光谱来看，窄带蓝光刺激了长波长敏感和短波长敏感视锥细胞，但相对激活不会随屈光状态而变化。这消除了纵向色差的反馈，而纵向色差反馈可能对维持正视状态至关重要。
